Compost: How to Make it and How Much to Use

Why Compost?

Composting is well-suited to agriculture. Farms produce an abundance of organic wastes and land availability for compost piles usually isn't a problem. Farmers who decide to compost can reap many benefits from the finished product. Compost is a valuable soil conditioner that enhances soil structure. The organic matter in compost improves soil nutrient-holding and water-retaining capabilities which, in turn, reduces fertilizer requirements and erosion while enhancing soil tilth.

A large fraction of the waste stream is comprised of organic residuals that can be turned from a waste into a useful soil amendment through composting. There is a broad range of residual sources used in compost including manure, yard and food wastes, and animal mortalities and a wide array of people and groups composting including households, schools, farms, municipalities and private entities. Whether your composting operation is small or large the same principles apply: the proper materials, surface area, volume, moisture, aeration, time and temperature will affect the outcome of your compost.

How to Make Compost

There are several composting systems farmers can choose from if they decide to start composting. The options vary in cost, labor requirements, and processing time.

Windrow composting

while it is the most common method, is also the most labor-intensive. Windrow composting involves stacking raw materials into long piles that are turned regularly with a front-end loader, bucket loader or special compost turner. The advantages of windrow composting are that it requires no source of electricity; windrows can be built in the fields, where the compost will be used; and farmers can usually use existing equipment to make and maintain the piles. On the other hand, farmers must monitor the pile temperature often to avoid odor problems and ensure that the ingredients are composting.

Passively aerated-pile composting

involves placing the mix of raw materials in piles on top of a bed of coarse materials, such as wood chips. A network of pipes runs through the coarse materials to provide aeration. The advantages of passively aerated piles are that they require less labor than windrow composting and no electricity. This method, however, takes longer to complete.

Aerated static-pile composting

is similar to the passively aerated method, except air is forced through the aeration pipes mechanically. As a result, static piles require a source of power.

In-vessel composting

is the most expensive method. Two types of units sometimes found on farms are bin composters and agitated-bed, or channel, composters. With bin composting, raw materials are placed in bins similar to grain bins or a bulk storage building. The materials are seldom turned, if at all, and are aerated by forced aeration from the bottom of the bin. With channel composters, raw materials are placed in channels. The materials are turned regularly via a machine that travels on a track above the channels. Most channel composters also have aeration pipes. In-vessel compost systems require a substantial initial investment and a higher level of knowledge and skill on the farmer's part.

Tips for Using Compost

Avoid the continuous use of compost or any single organic nutrient source containing more than one nutrient. Instead, use a variety of nutrient sources. This will help avoid reaching soil nutrient levels exceeding crop needs.

Soil test to keep track of soil nutrient levels. If levels exceed crop needs, avoid using compost. Instead, use a nutrient source that has no or minimal levels of the nutrient(s) in excess. One exception to this tip is that starter phosphorus may be needed for some crops when soils are cold in early spring, even when soil phosphorus levels exceed crop needs.

Test your compost. Composts differ in their chemical analysis. By having it tested, it can be more accurately applied.

Calculate the amount of compost to apply. This is commonly based on the nitrogen needs of the crop unless phosphorus levels exceed crop needs. When phosphorus levels are high, calculate both phosphorus- and nitrogen-based application rates and use the lower of the two. This practice will help avoid over application and its associated costs: the cost of the compost, environmental costs, and loss of profits due to compromised plant health.

Incorporate compost in the soil. This will promote the mineralization process and minimize runoff and erosion losses.

If phosphorus levels exceed crop needs or it is suspected that nitrogen levels are high, minimize losses through erosion, runoff, and leaching. Environmental concerns develop when phosphorus and nitrogen reach bodies of water. Minimizing erosion by planting cover crops, using reduced tillage practices, or using grass waterways to catch and infiltrate runoff from a field can curtail movement of these nutrients.

Compost is very beneficial to soils, but over application of compost can create soil nutrient imbalances that need to be monitored and managed.